It uses two radios and two antennas. It takes a toll on battery life. Verizon could address this by implementing VoLTE, which would benefit everyone using an LTE phone, including you, since it would shut off the CDMA radio entirely. They could also implement CDMA Rev B, which supports SVDO over CDMA.
It's a curious decision by Apple, to be sure, but I can understand the technical reasons for making that design choice (Apple wants to use a single more advanced chip than two less advanced chips to save space and battery life).
Anyway, I'm on AT&T, so I don't really care as I could do this years ago.